In view of dwindling supplies of traditional diesel fuels, it would be very advantageous if compression-ignition engines, more particularly direct fuel injection types, could be easily modified and adapted to burn more plentiful alternative fuels such as 100 percent methanol or ethanol. Such alternative fuels are regarded as attractive substitutes for conventional diesel fuels because methanol can be feasibly synthesized from a wide variety of substances such as coal, natural gas, wood, or animal waste and ethanol can be feasibly produced by fermentation of starch derived from widely grown plants such as sugar cane or corn. Moreoever, the amounts of nitrogen oxides and particulates are naturally lower and practically nonexistent, respectively, when burning such alcohol fuels as compared to burning traditional diesel fuels.
However, these alternative fuels are characterized by a cetane number or ignition value on the order of about 0-10 whereas traditional diesel fuels, such as Grade 2-D diesel fuel, are characterized by a cetane number of at least 40. Consequently, unlike traditional diesel fuels, these relatively lower-cetane-number alternative fuels do not autoignite under normal compression ratios in a compression-ignition engine merely by contacting and mixing with intake air which has been compressed in the combustion chamber by a piston and thereby typically heated to about 538.degree. C. (1000.degree. F.)
Such relatively lower-cetane-number alternative fuels can be locally ignited with the aid of an electrically-energized spark plug or glow plug which directly heats the fuel to a sufficiently elevated temperature of about 1000.degree. C. (1832.degree. F.) However, another major problem exists of completely igniting and burning all of the alternative fuel that is directly injected into the combustion chamber. This problem is due to the way fuel has been typically directly injected into the combustion chamber of a compression-ignition engine.
As shown in U.S. Pat. No. 4,275,844 issued to Grgurich et al on June 30, 1981, a conventional open combustion chamber of a direct injection compression-ignition engine typically includes a high pressure fuel injection nozzle having very small orifices. The orifices periodically spray a plurality of distinct and evenly spaced high pressure fuel streams to generally all sectors of the open combustion chamber which is already periodically filled with fresh intake air. This pattern of relatively concentrated conical fuel streams separated by pockets of intake air, similar to the radial spokes of a wheel, is desirable for direct injection engines to enable the fuel streams to quickly penetrate, atomize, mix and combust with the required relatively larger amounts of intake air before each cyclic power stroke of the open combustion chamber has substantially begun.
If a glow plug or spark plug is energized to produce a localized temperature of about 1000.degree. C. (1832.degree. F.) and is positioned in close enough proximity to one of the mutually spaced fuel streams of relatively lower-cetane-number alternative fuel, only that one fuel stream and perhaps other nearest fuel streams will ignite. However, the fuel-deficient air pockets separating each of the other remotely spaced fuel streams will prevent the flame from burning directly and rapidly to those other fuel streams. Consequently, the fuel streams which are not ignited or are only partially ignited are exhausted from the open combustion chamber as either wasted raw fuel or incompletely combusted fuel. This of course significantly and undesirably reduces the fuel economy and power output of the engine and raises the level of noxious emissions, particularly hydrocarbons, exhausted from the open combustion chamber.
The glow plug or spark plug perhaps could be over energized to produce a very high temperature which is much higher than 1000.degree. C. (1832.degree. F.) such that all of the fuel streams are sufficiently heated and directly ignited. However, this approach is very undesirable because, for example, the life of the glow plug or spark plug is thereby drastically shortened.
The present invention is directed to overcoming one or more of the problems as set forth above.